The goal of the proposed research aligns with the Musculoskeletal Disorders Strategic Goal 7.0 in the National Construction Agenda of the National Occupational Research Agenda to reduce the incidence and severity of work-related musculoskeletal disorders among construction workers in the U.S. Based on U.S. Bureau of Labor statistics and published epidemiological data, an estimated 1.5 million workers use powered tools in the construction, manufacturing, agriculture-forestry and fishing, and mining Sectors and are currently exposed to levels of hand-arm vibration putting them at risk for developing hand-arm vibration syndrome (HAVS) with a prevalence of 10-50% after working 10 years. The major nerve and artery pathologies of HAVS are debilitating numbness and reduced blood flow in the fingers. The Approach: Exposing humans to damaging vibration in a research study is unethical so animal model surrogates with nerves and arteries similar in structure and function to those in human fingers are essential. Two rat-tail vibration models are utilized: one simulating the sinusoidal and the other simulating impulse shock wave components of hand-arm vibration. The risk factors of vibration frequency (Hz), acceleration (m/s2 r.m.s.), amplitude (mm) and duration (vibration/day and days of vibration) that lead to HAVS are assessed. Our newly developed, impulse shock wave model delivers vibration with 0.5 Hz to over 21 kHz components from a riveting hammer that generates shock wave vibration characteristic of many impact tools. Shock wave vibration injury, recognized over 90 years ago, has been neglected. This knowledge gap must be addressed because severe HAVS can onset in 2.5 months compared to taking years to develop from non-impact powered tools. Sinusoidal vibration has been the major focus of vibration research because most tools have a dominant frequency in the 30-250 Hz range to which most HAVS has been attributed. Overlooked is the fact that non-impact tools generate shock waves albeit less regularly. Impact tools, such as riveting hammers, chippers, stone cutters, impact drills and road breakers, generate shock wave pulses with each duty cycle. The proposed studies of the vibrated rat-tail investigate quantitatively the relationships of frequency, acceleration, amplitude and duration to structural damage of the innervation of skin, artery and skeletal muscle and the functional deficits related to loss of feeling and muscle weakness (nerve conduction velocity, von Frey touch perception, thermal sensitivity, and cold immersion provocation rewarming and return of blood flow). The proposed research investigates 4 aims: Aim 1 To investigate the dose response of duration, frequency, acceleration and amplitude on the induction of persistent vasoconstriction in the rat-tail sinusoidal vibration model, Aim 2 To define the dose response relationship of shock wave vibration exposure duration with the levels of nerve and artery tissue injury, Aim 3 To evaluate by repeated measures the occurrence and recoverability of vibration-induced functional deficits in the innervation and blood supply of the rat-tail following 12 minute shock wave vibration per day for 1 day, 1 week and 10 weeks, and Aim 4 To evaluate the occurrence and recoverability of vibration-induced structural deficits in the innervation and blood supply of the rat-tail following 12 minute shock wave vibration per day for 1 day, 1 week and 10 weeks. Challenge to existing paradigm: The need for data on shock vibration is critical because the existing International Standard ISO 5349 does not take into account impulse vibration and high frequency components in risk calculation, and therefore, the Standard seriously underestimates the harm to workers. ISO 5349 attenuates high frequency contribution because of studies reporting that humans do not feel vibrations >1000 Hz. Expected outcomes: The proposed research will demonstrate that what you can't feel can hurt you. The dose response data will aid development of evidenced-base guidelines for protecting workers and challenge manufacturers to eliminate offensive vibration. Our collaborator, Dr. Dong, at the NIOSH HELD research laboratory Morgantown, WV will test the efficacy of antivibration glove protection and develop new engineering methods to measure shock vibration in the workplace so that exposure can be monitored. Changing barriers to workplace protection: The results of the proposed research will advance the understanding of the dose response relationships of sinusoidal and shock wave vibration to tissue injury. These data will guide development of interventions that lower risk of hand arm vibration injury in the workplace.